Digiscoping in such low early-morning light resulted in poor images, but this one gives an idea of what we were looking at.
Later in the morning Jeremiah Trimble relocated what looked to be the same bird right in the cove next to the parking lot where we had some great looks including a short flight. Jeremiah captured some nice images of the open wing.
Several classic Thayer's features on this bird: smaller than HEGU size (seen in the field), delicate head/bill combo, faintly masked face, entirely juvenal scapulars, solidly mid-brown tertials, and chocolate-brown primaries with thin frosty tips.
In speaking with Jeremiah and Rick Heil, plus doing some research, it appears that this amount of pale at the base of the bill is OK for Thayer's in mid-late Jan.